Phase-change random access memory devices and methods of manufacturing the same

ABSTRACT

A PRAM device includes a lower electrode, a phase-change nanowire and an upper electrode. The phase-change nanowire may be electrically connected to the lower electrode and includes a single element. The upper electrode may be electrically connected to the phase-change nanowires.

PRIORITY STATEMENT

This application is a divisional application of U.S. application Ser.No. 12/801,450, filed on Jun. 9, 2010, now allowed, which claimspriority under 35 USC §119 to Korean Patent Application No.10-2009-0055763, filed on Jun. 23, 2009, in the Korean IntellectualProperty Office (KIPO), the entire contents of which are hereinincorporated by reference.

BACKGROUND

1. Field

Example embodiments relate to phase-change random access memory (PRAM)devices and methods of manufacturing the same. More particularly,example embodiments relate to PRAM devices including a single-elementphase-change material (PCM) and methods of manufacturing the same.

2. Description of the Related Art

PRAM devices having a multi-element, e.g., germanium-antimony-tellurium(GST), PCM layer may not be reliable because the antimony of the GST PCMlayer may be extracted in a repetitive operation of rewriting, e.g.,crystallization, and vice versa. Thus, developing PRAM devices havingmore reliability is needed.

SUMMARY

Example embodiments provide PRAM devices and methods of manufacturingPRAM devices having improved reliability.

According to example embodiments, there is provided a phase-changerandom access memory (PRAM) device. The PRAM device may include a lowerelectrode, a phase-change nanowire and an upper electrode. Thephase-change nanowire may include a single element and may beelectrically connected to the lower electrode. The upper electrode maybe electrically connected to the phase-change nanowires.

In example embodiments, the phase-change nanowire may be formed within aporous insulation layer between the lower and upper electrodes. Inexample embodiments, the phase-change nanowire may be formed in a poreof the porous insulation layer having a cross-section in a range ofabout 1×1 nm² to about 5×5 nm².

In example embodiments, the PRAM device may further include aphase-change material (PCM) layer between the porous insulation layerand the upper electrode. In example embodiments, the PCM layer may beformed integrally with the phase-change nanowire and includes the samematerial as that of the phase-change nanowire.

In example embodiments, the porous insulation layer may include asilsesquioxane (SSQ)-based material, a polymer having a nonpolarcarbon-carbon bond, or a silica-based material. In example embodiments,the SSQ-based material may include hydrogen silsesquioxane (HSQ).

In example embodiments, the phase-change nanowire may include antimonyor bismuth. In example embodiments, the PRAM device may further includea diode electrically connected to the lower electrode. In exampleembodiments, the phase-change nanowire may have a diameter of less thanabout 10 nm.

In example embodiments, the lower and upper electrodes may include atleast one of a conductive material and a conductive carbon-basedmaterial. The conductive material may be at least one of titanium,tantalum, tungsten, molybdenum, niobium, titanium nitride, tantalumnitride, tungsten nitride, molybdenum nitride, niobium nitride,molybdenum aluminum nitride, tungsten boron nitride, titaniumoxynitride, tungsten oxynitride and tantalum oxynitride.

According to example embodiments, there is provided a method ofmanufacturing a phase-change random access memory (PRAM) device. In themethod, a lower electrode may be formed through an insulation layer. Aphase-change nanowire may be formed using a single element to beelectrically connected to the lower electrode. An upper electrode may beformed to be electrically connected to the phase-change nanowire.

In example embodiments, when the phase-change nanowire is formed, aporous insulation layer may be formed on the lower electrode; and thephase-change nanowire may be formed in a pore of the porous insulationlayer having a cross-section in a range of about 1×1 nm² to about 5×5nm². In example embodiments, when the phase-change nanowire is formed,an atomic layer deposition (ALD) process may be performed on the porousinsulation layer using a single element. In example embodiments, the ALDprocess may be performed using antimony or bismuth. In exampleembodiments, the ALD process may be performed using Sb-(iPr)₃ as aprecursor source gas. In example embodiments, the ALD process may beperformed using argon plasma.

In example embodiments, the method may further include forming aphase-change material (PCM) layer between the porous insulation layerand the upper electrode. In example embodiments, the PCM layer may beformed integrally with the phase-change nanowire and may include thesame material as that of the phase-change nanowire.

In example embodiments, forming the porous insulation layer may includeforming any one selected from the group consisting of a silsesquioxane(SSQ)-based material, a polymer having a nonpolar carbon-carbon bond,and a silica-based material. In example embodiments, the SSQ-basedmaterial may include hydrogen silsesquioxane (HSQ).

In example embodiments, the method may further include forming a diodeto be electrically connected to the lower electrode. In exampleembodiments, the phase-change nanowire may be formed to have a diameterof less than about 10 nm. In example embodiments, forming the lower andupper electrodes may include forming at least one of a conductivematerial and a conductive carbon-based material. In example embodiments,the conductive material may be at least one of titanium, tantalum,tungsten, molybdenum, niobium, titanium nitride, tantalum nitride,tungsten nitride, molybdenum nitride, niobium nitride, molybdenumaluminum nitride, tungsten boron nitride, titanium oxynitride, tungstenoxynitride and tantalum oxynitride.

According to example embodiments, a PRAM device may include aphase-change nanowire having a single element, and thus, some elementstherein may not be segregated from other elements. Thus, no phasesegregation may occur in the phase-change nanowire, and the PRAM devicemay have improved reliability. Additionally, the phase-change nanowiremay have a smaller contact area with a lower electrode, and thus, asmaller current may be needed to operate the PRAM device. As a result,the PRAM device may have a higher operation speed.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings. FIGS. 1 to 25 represent non-limiting, example embodiments asdescribed herein.

FIG. 1 is a cross-sectional view illustrating a phase-change randomaccess memory (PRAM) device in accordance with example embodiments;

FIG. 2 is a timing chart illustrating a method of forming thephase-change nanowire 135 and the PCM layer 130;

FIG. 3A is a photograph showing a cross-section of a PCM layer includingantimony formed by performing 22 cycles of the above steps at atemperature of about 250° C.;

FIG. 3B is a photograph showing a cross-section of a PCM layer includingantimony formed by performing 25 cycles of the above steps at atemperature of about 100° C.;

FIG. 4 is a photograph showing a cross-section of a porous insulationlayer having phase-change nanowires including antimony therein, and agraph showing antimony and titanium in the porous insulation layer;

FIG. 5 is a graph showing changes of a resistance, a current and avoltage of the PRAM device including the phase-change nanowires when thephase of the phase-change nanowires is changed several times;

FIGS. 6 to 21 are cross-sectional views illustrating a method ofmanufacturing a PRAM device in accordance with example embodiments;

FIGS. 22 to 24 are cross-sectional views illustrating a method ofmanufacturing a PRAM device in accordance with other exampleembodiments; and

FIG. 25 is a diagram illustrating a communication system including thePRAM device in accordance with example embodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Various example embodiments will be described more fully hereinafterwith reference to the accompanying drawings, in which some exampleembodiments are shown. The present inventive concept may, however, beembodied in many different forms and should not be construed as limitedto example embodiments set forth herein. Rather, these exampleembodiments are provided so that this description will be thorough andcomplete, and will fully convey the scope of the present inventiveconcept to those skilled in the art. In the drawings, the sizes andrelative sizes of layers and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numerals refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present inventive concept.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized example embodiments (and intermediate structures). As such,variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, example embodiments should not be construed as limitedto the particular shapes of regions illustrated herein but are toinclude deviations in shapes that result, for example, frommanufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the figures are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to limit the scope ofthe present inventive concept.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein. Hereinafter, example embodiments will beexplained in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view illustrating a phase-change randomaccess memory (PRAM) device in accordance with example embodiments.Referring to FIG. 1, the PRAM device may include a lower electrode 110,a phase-change nanowire 135 and an upper electrode 140. The PRAM devicemay further include a porous insulation layer 120 and a phase-changematerial (PCM) layer 130.

The lower electrode 110 may be formed through an insulation layer 100 ona substrate (not shown). The lower electrode 110 may include aconductive material, e.g., titanium, tantalum, tungsten, molybdenum,niobium, titanium nitride, tantalum nitride, tungsten nitride,molybdenum nitride, niobium nitride, molybdenum aluminum nitride,tungsten boron nitride, titanium oxynitride, tungsten oxynitride and/ortantalum oxynitride, and/or a conductive carbon-based material. Thesemay be used alone or in a combination thereof.

The porous insulation layer 120 may be formed on the insulation layer100 and the lower electrode 110. The porous insulation layer 120 mayinclude a silsesquioxane (SSQ)-based material, e.g., hydrogensilsesquioxane (HSQ), a polymer having a nonpolar carbon-carbon bond, ora silica-based material. The porous insulation layer 120 may include apore having a diameter of less than about 10 nm. In example embodiments,the pore in the porous insulation layer 120 may have a cross-section ofabout 1×1 nm² to about 5×5 nm².

The phase-change nanowire 135 may include a single element. For example,the phase-change nanowire 135 may include antimony or bismuth. Thephase-change nanowire 135 may be formed in the porous insulation layer120, and may be electrically connected to the lower electrode 110.Particularly, the phase-change nanowire 135 may be formed in the pore ofthe porous insulation layer 120. The pore may have a relatively smallcross-section, and thus, the phase-change nanowire 135 may also have arelatively small cross-section, e.g., in a range of about 1×1 nm² toabout 5×5 nm². As a result, the phase-change nanowire 135 may have avery small contact area with the lower electrode 110, and thus, the PRAMdevice may have a very large current density flowing through thephase-change nanowire 135.

The PCM layer 130 may be formed integrally with the phase-changenanowire 135, and may include substantially the same material as that ofthe phase-change nanowire 135. The upper electrode 140 may beelectrically connected to the phase-change nanowire 135. For example,the upper electrode 140 may be formed on the porous insulation layer120, and may be electrically connected to the phase-change nanowire 125.When the PRAM device has the PCM layer 130, the upper electrode 140 maybe formed on the PCM layer 130.

The upper electrode 140 may include a conductive material, e.g.,titanium, tantalum, tungsten, molybdenum, niobium, titanium nitride,tantalum nitride, tungsten nitride, molybdenum nitride, niobium nitride,molybdenum aluminum nitride, tungsten boron nitride, titaniumoxynitride, tungsten oxynitride and/or tantalum oxynitride, and/or aconductive carbon-based material. These may be used alone or in acombination thereof.

The phase-change nanowire 135 and the PCM layer 130 may include thesingle element, and thus, some elements therein may not be segregatedfrom other elements. Thus, no phase segregation may occur in thephase-change nanowire 135 and the PCM layer 130, and the PRAM device mayhave improved reliability. Additionally, the phase-change nanowire 135may have a smaller area in contact with the lower electrode 110, andthus, a smaller current may be needed to operate the PRAM device. As aresult, the PRAM device may have a higher operation speed.

FIG. 2 is a timing chart illustrating a method of forming thephase-change nanowire 135 and the PCM layer 130. The method may includean atomic layer deposition (ALD) process as follows. Referring to FIGS.1 and 2, during a first time period Ts, a precursor source gas andplasma may be provided into a chamber (not shown), and a phase-changelayer may be formed on the porous insulation layer 120 and in the poreof the porous insulation layer 120. The precursor source gas may includeSb-(iPr)₃. Examples of the precursor source gas may include Sb-(Et)₃,Sb-(n-Pr)₃, Sb-(t-Bu)₃ and/or Sb-(i-Bu)₃. A carrier gas, e.g., argongas, may be also provided into the chamber. The chamber may have aninternal temperature of about 100 to about 300° C.

After providing a purge gas into the chamber during a second timeperiod, during a third time period Tp, a reducing agent gas, e.g.,hydrogen or ammonia, and plasma may be provided into the chamber. Apurge gas may be provided into the chamber again during a fourth timeperiod. The purge gas may include argon gas, and may be provided intothe chamber at a flow rate ratio of about 1000 sccm.

One cycle may include the above steps, and may be repeatedly performedto form the phase-change nanowire 135 and the PCM layer 130 in the poreand on the porous insulation layer 120, respectively. In exampleembodiments, about 20 to about 30 cycles may be performed, and the PCMlayer 130 may be formed to have a thickness of about 10 nm. A heattreatment may be performed on the substrate, and the phase-changenanowire 135 and the PCM layer 130 may be crystallized.

FIG. 3A is a photograph showing a cross-section of a PCM layer includingantimony formed by performing 22 cycles of the above steps at atemperature of about 250° C. The surface of the PCM layer was veryrough. FIG. 3B is a photograph showing a cross-section of a PCM layerincluding antimony formed by performing 25 cycles of the above steps ata temperature of about 100° C. The surface of the PCM layer was smooth.

As shown in FIGS. 3A and 3B, when the temperature of the chamber is morethan about 150° C., the surface of the PCM layer is rough. However, whenthe temperature of the chamber is less than about 150° C., the surfaceof the PCM layer is smoother.

FIG. 4 is a photograph showing a cross-section of a porous insulationlayer having phase-change nanowires including antimony therein, and agraph showing antimony and titanium in the porous insulation layer.Particularly, the photograph shows a layer structure including a siliconlayer, a silicon oxide layer, a titanium nitride layer, an HSQ layer andan antimony layer sequentially stacked.

Referring to FIG. 4, antimony is uniformly distributed in the HSQ layer,i.e., the porous insulation layer to a depth of about 50 nm from a topsurface thereof, and titanium is also distributed at a depth of about100 to about 150 nm in the titanium nitride layer, i.e., a lowerelectrode. Thus, the phase-change nanowires including antimony may beuniformly formed through the porous insulation layer by the ALD processin accordance with example embodiments.

FIG. 5 is a graph showing changes of a resistance, a current and avoltage of the PRAM device including the phase-change nanowires when thephase of the phase-change nanowires is changed several times.

Referring to FIG. 5, a ratio of a reset resistance to a set resistanceis more than about 10 at a reset current of about 1.5 mA, and thechanges of the resistance, the current and the voltage are uniform.Thus, the PRAM device may have improved reliability.

FIGS. 6 to 21 are cross-sectional views illustrating a method ofmanufacturing a PRAM device in accordance with example embodiments.Referring to FIG. 6, a pad oxide layer 205 and a pad nitride layer 210may be sequentially formed on a substrate 200. The substrate 200 may bedivided into a cell region A and a peripheral region B. In exampleembodiments, the pad oxide layer 205 may be formed to have a thicknessof about 100 to about 150 Å by a thermal oxidation process, and the padnitride layer 210 may be formed to have a thickness of about 1,000 toabout 1,100 Å by a chemical vapor deposition (CVD) process. In exampleembodiments, the pad nitride layer 210 may be formed by forming a firstnitride layer (not shown) having a thickness of about 300 Å and forminga second nitride layer (not shown) having a thickness of about 700 toabout 800 Å. The pad oxide layer 205 may absorb the stress of the padnitride layer 210, and may protect the substrate 200 therefrom.

A hard mask layer (not shown) may be further formed on the pad nitridelayer 210. In example embodiments, the hard mask layer may be formed tohave a multi-stack structure. For example, an oxide layer or a nitridelayer may be formed on the pad nitride layer 210, an organic layer maybe formed on the oxide layer or the nitride layer, and ananti-reflective layer may be formed on the organic layer.

Referring to FIG. 7, a photoresist pattern (not shown) may be formed onthe hard mask layer. The hard mask layer may be patterned using thephotoresist pattern as an etching mask to form a hard mask (not shown).The photoresist pattern may be removed by an ashing process and/or anetch back process. The pad nitride layer 210 and the pad oxide layer 205may be patterned using the hard mask. Upper portions of the substrate200 may be removed using the pad nitride layer 210 and the pad oxidelayer 205 as an etching mask to form a plurality of trenches (notshown). The trenches may be formed to have a depth of about 2000 toabout 5000 Å. The trenches may be formed to have sidewalls angled withrespect to a vertical direction, so that the stress of an isolationlayer 215 filled into the trenches subsequently on the substrate 200 maybe reduced. In example embodiments, some of the trenches in the cellregion A may be less spaced apart from each other than those of theperipheral region B.

In example embodiments, the isolation layer 215 may be formed asfollows. Particularly, exposed portions of the substrate 200 near thetrenches may be thermally oxidized. A first oxide layer may be formed oninner walls of the trenches to have a thickness of about 100 Å using amiddle temperature oxide (MTO). A second oxide layer may be formed onthe first oxide layer to fill the remaining portions of the trenchesusing high density plasma chemical vapor deposition (HDP-CVD) oxide.After removing the hard mask, the pad nitride layer 210 and the padoxide layer 205, an upper portion of the second oxide layer may beplanarized until a top surface of the substrate 200 is exposed. Thus,the isolation layer 215 including the first and second oxide layers maybe formed in the trenches.

In example embodiments, before forming the trenches, impurities may beimplanted into the substrate 200 so that the isolation layer 215 may beisolated from active regions of the substrate 200 more clearly.Additionally, impurities may be implanted into the substrate 200 to forma well region or an impurity region therein (not shown).

Referring to FIG. 8, a gate insulation layer 220 may be formed on thesubstrate 200 and the isolation layer 215. Gate electrodes 225 may beformed on the gate insulation layer 220 in the peripheral region B.First impurities may be implanted into the peripheral region B of thesubstrate 200 to form a first impurity region (not shown) at upperportions of the substrate 200 adjacent to the gate electrodes 225.

Referring to FIG. 9, gate spacers 230 may be formed on sidewalls of thegate electrodes 225. The gate spacers 230 may be formed using a nitrideby a CVD process and an etch back process. First impurities may belightly implanted into the peripheral region B of the substrate 200using the gate electrodes 225 as an ion implantation mask to form firstimpurity regions (not shown) at upper portions of the substrate 200adjacent to the gate electrodes 225. Gate spacers 230 may be formed onsidewalls of the gate electrodes 225. Second impurities may be heavilyimplanted into the peripheral region B of the substrate 200 using thegate electrodes 225 and the gate spacers 230 as an ion implantation maskto form second impurity regions (not shown) at upper portions of thesubstrate 200 adjacent to the gate electrodes 225. The first and secondimpurity regions may form source/drain regions 235 having a lightlydoped drain (LDD) structure.

Referring to FIG. 10, a portion of the gate insulation layer 220 in thecell region A may be removed, and a mask (not shown) covering theperipheral region B may be formed on the substrate 200. A conductivelayer 240 may be formed at an upper portion of the substrate 200 in thecell region A. In example embodiments, the conductive layer 240 may beformed by implanting impurities, e.g., n-type impurities, into thesubstrate 200. The conductive layer 240 may serve as a word line.

Referring to FIG. 11, a first insulating interlayer 245 and a secondinsulating interlayer 250 may be sequentially formed on the substrate200 and the isolation layer 215 to cover the gate electrodes 225, thegate spacers 230, the gate insulation layer 220 and the conductive layer240. The first and second insulating interlayers 245 and 250 may beformed using HDP-CVD oxide and a nitride, respectively. The first andsecond insulating interlayers 245 and 250 may be formed to havethicknesses of about 5000 Å and 1500 Å, respectively.

Referring to FIG. 12, openings 255 may be formed through the first andsecond insulating interlayers 245 and 250 to expose portions of theconductive layer 240. Spacers (not shown) may be further formed onsidewalls of the openings 255. A cleaning process may be furtherperformed on the exposed portions of the conductive layer 240.

Referring to FIG. 13, a single crystalline silicon layer may be formedon the exposed portion of the conductive layer 240 in the openings 255by an epitaxial growth process. In example embodiments, the singlecrystalline silicon layer may be grown to cover a top surface of thesecond insulating interlayer 250, and an upper portion of the singlecrystalline silicon layer may be planarized until the top surface of theconductive layer 240 is exposed.

Third and fourth impurities may be sequentially implanted into thesingle crystalline silicon layer to form a lower conductive layer 260and an upper conductive layer 265, respectively. The lower and upperconductive layers 260 and 265 may form a diode 267. In exampleembodiments, the third and fourth impurities may include n-typeimpurities and p-type impurities, respectively. In example embodiments,an upper portion of the upper conductive layer 265 may be removed by anetch back process.

Referring to FIG. 14, a lower electrode 270 may be formed on the diode267. The lower electrode 270 may be formed using a conductive material,e.g., titanium, tantalum, tungsten, molybdenum, niobium, titaniumnitride, tantalum nitride, tungsten nitride, molybdenum nitride, niobiumnitride, molybdenum aluminum nitride, tungsten boron nitride, titaniumoxynitride, tungsten oxynitride and/or tantalum oxynitride, and/or aconductive carbon-based material. These may be used alone or in acombination thereof.

Referring to FIG. 15, a porous insulation layer 275 may be formed on thelower electrode 270. The porous insulation layer 275 may be formed usinga silsesquioxane (SSQ)-based material, e.g., hydrogen silsesquioxane(HSQ), a polymer having a nonpolar carbon-carbon bond, or a silica-basedmaterial. The porous insulation layer 275 may be formed by a spincoating process, a CVD process, an ALD process or a PVD process. Theporous insulation layer 275 may include a pore having a diameter of lessthan about 10 nm. In example embodiments, the pore in the porousinsulation layer 275 may have a cross-section of about 1×1 nm² to about5×5 nm².

A PCM layer 280 may be formed on the porous insulation layer 275 usingantimony or bismuth by an ALD process. When the PCM layer 280 is formed,a phase-change nanowire (not shown) may be formed through the porousinsulation layer 275, e.g., in the pore thereof. The phase-changenanowire may include a single element. For example, the phase-changenanowire may include antimony or bismuth. The phase-change nanowire maybe formed through the porous insulation layer 275, and may beelectrically connected to the lower electrode 270. Particularly, thephase-change nanowire may be formed in the pore of the porous insulationlayer 275. The pore may have a relatively small cross-section, and thus,the phase-change nanowire may also have a relatively smallcross-section, e.g., in a range of about 1×1 nm² to about 5×5 nm². As aresult, the phase-change nanowire may have a relatively small contactarea with the lower electrode 270, and thus, the PRAM device may have arelatively large current density flowing through the phase-changenanowire.

Referring to FIG. 16, an upper electrode 285 may be formed on the PCMlayer 280 and the second insulating interlayer 250 to be electricallyconnected to the phase-change nanowire. The upper electrode 285 may beformed using a conductive material, e.g., titanium, tantalum, tungsten,molybdenum, niobium, titanium nitride, tantalum nitride, tungstennitride, molybdenum nitride, niobium nitride, molybdenum aluminumnitride, tungsten boron nitride, titanium oxynitride, tungstenoxynitride and/or tantalum oxynitride, and/or a conductive carbon-basedmaterial. These may be used alone or in a combination thereof.

A capping layer (not shown) may be further formed on the upper electrode285. The capping layer may be formed using a nitride and aluminum oxide.The capping layer may prevent or reduce impurities in a third insulatinginterlayer 290 subsequently formed from moving to the PCM layer 280.

Referring to FIG. 17, the third insulating interlayer 290 may be formedon the second insulating interlayer 290 to cover the upper electrode285. In example embodiments, the third insulating interlayer 290 may beformed using plasma-tetraethyl orthosilicate (P-TEOS) to have athickness of about 3000 Å.

The first, second and third insulating interlayers 245, 250 and 290 andthe gate insulation layer 220 may be partially removed to form firstcontact holes (not shown) therethrough. A first barrier layer 295 may beformed on inner walls of the first contact holes. The first barrierlayer 295 may be formed using a metal or metal nitride, e.g., titanium,titanium nitride and/or titanium tungsten. A first metal layer 300 maybe formed on the barrier layer 295 to fill the remaining portions of thefirst contact holes. In example embodiments, the first metal layer 300may be formed using tungsten. The first barrier layer 295 and the firstmetal layer 300 may be referred to as a first contact plug 301. A fourthinsulating interlayer 305 may be formed on the third insulatinginterlayer 290 and the first contact plug 301.

Referring to FIG. 18, second contact holes 310 may be formed through thefourth insulating interlayer 305 and the third insulating interlayer 290to expose the first contact plug 301 and the upper electrode 285.

Referring to FIG. 19, a second barrier layer 320 may be formed on innerwalls of the second contact holes. The second barrier layer 320 may beformed using a metal or metal nitride e.g., titanium, titanium nitrideand/or titanium tungsten. A second metal layer 325 may be formed on thesecond barrier layer 320 to fill the remaining portions of the secondcontact holes 310. In example embodiments, the second metal layer 325may be formed using tungsten. The second barrier layer 320 and thesecond metal layer 325 may be referred to as a second contact plug.

Referring to FIG. 20, a first wiring 330 may be formed on the secondcontact plug and the fourth insulating interlayer 305. The first wiring330 may be formed using e.g., aluminum. In example embodiments, thefirst wiring 330 may be formed to have a multi-stack structure includinga metal layer and a capping layer (not shown).

A fifth insulating interlayer 335 may be formed on the fourth insulatinginterlayer 305 to cover the first wiring 330. The fifth insulatinginterlayer 335 may be formed using HDP-CVD oxide and/or P-TEOS.

Referring to FIG. 21, a second wiring 340 may be formed through thefifth insulating interlayer 335 to be electrically connected to thefirst wiring 330. The second wiring 340 may be formed using a metal. Aprotection layer 345 may be formed on the fifth insulating interlayer335 to cover the second wiring 340.

The phase-change nanowire and the PCM layer 280 may include the singleelement, and thus, some elements therein may not be segregated fromother elements. Thus, no phase segregation may occur in the phase-changenanowire and the PCM layer 280, and the PRAM device may have improvedreliability. Additionally, the phase-change nanowire may have arelatively small contact area with the lower electrode 270, and thus, asmall current may be needed to operate the PRAM device. As a result, thePRAM device may have a higher operation speed.

FIGS. 22 to 24 are cross-sectional views illustrating a method ofmanufacturing a PRAM device in accordance with other exampleembodiments. The PRAM device of FIGS. 22 to 24 are substantially thesame as that of FIGS. 6 to 21 except for the shape of the porousinsulation layer 275 and the PCM layer 280. Thus, like numerals refer tolike elements, and repetitive explanations are omitted here. Referringto FIG. 22, processes substantially the same as those illustrated withreference to FIGS. 6 to 14 may be performed to form the structure ofFIG. 22.

Referring to FIG. 23, a porous insulation layer 475 may be formedconformally on the lower electrode 270 and inner walls of the openings255. A PCM layer 480 may be formed on the porous insulation layer 475 tofill the remaining portions of the openings 255. When the PCM layer 480is formed, a phase-change nanowire (not shown) may be formed through theporous insulation layer 475. Referring to FIG. 24, processessubstantially the same as those illustrated with reference to FIGS. 16to 21 may be performed to form the structure of FIG. 24.

FIG. 25 is a diagram illustrating a communication system including thePRAM device in accordance with example embodiments. Referring to FIG.25, a communication system 600 may include a sensor module 610, a globalpositioning system (GPS) 615 and a cellular phone 620. In thecommunication system 600, the sensor module 610, the GPS 615 and thecellular phone 620 may transfer data to each other, and thecommunication system 600 may transfer data with the data server 650 andthe base station 660. The cellular phone 620 may include the PRAM devicehaving an improved reliability and a higher operation speed, and thus,the communication system 600 may operate efficiently.

According to example embodiments, a PRAM device may include aphase-change nanowire having a single element, and thus, some elementstherein may not be segregated from other elements. Thus, no phasesegregation may occur in the phase-change nanowire, and the PRAM devicemay have improved reliability. Additionally, the phase-change nanowiremay have a relatively small contact area with a lower electrode, andthus, a smaller current may be needed to operate the PRAM device. As aresult, the PRAM device may have a higher operation speed.

The foregoing is illustrative of example embodiments and is not to beconstrued as limiting thereof. Although a few example embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in the example embodiments withoutmaterially departing from the novel teachings and advantages of thepresent inventive concept. Accordingly, all such modifications areintended to be included within the scope of the present inventiveconcept as defined in the claims. In the claims, means-plus-functionclauses are intended to cover the structures described herein asperforming the recited function and not only structural equivalents butalso equivalent structures. Therefore, it is to be understood that theforegoing is illustrative of various example embodiments and is not tobe construed as limited to the specific example embodiments disclosed,and that modifications to the disclosed example embodiments, as well asother example embodiments, are intended to be included within the scopeof the appended claims.

1. A phase-change random access memory (PRAM) device, comprising: alower electrode; a phase-change nanowire electrically connected to thelower electrode, the phase-change nanowire including a single element;and an upper electrode electrically connected to the phase-changenanowire.
 2. The PRAM device of claim 1, wherein the phase-changenanowire is within a porous insulation layer between the lower and upperelectrodes.
 3. The PRAM device of claim 2, wherein the phase-changenanowire is in a pore of the porous insulation layer having across-section in a range of about 1×1 nm² to about 5×5 nm².
 4. The PRAMdevice of claim 2, further comprising: a phase-change material (PCM)layer between the porous insulation layer and the upper electrode. 5.The PRAM device of claim 4, wherein the PCM layer is integral with thephase-change nanowire and includes the same material as that of thephase-change nanowire.
 6. The PRAM device of claim 2, wherein the porousinsulation layer includes any one selected from the group consisting ofa silsesquioxane (SSQ)-based material, a polymer having a nonpolarcarbon-carbon bond, and a silica-based material.
 7. The PRAM device ofclaim 6, wherein the SSQ-based material includes hydrogen silsesquioxane(HSQ).
 8. The PRAM device of claim 1, wherein the phase-change nanowireincludes antimony or bismuth.
 9. The PRAM device of claim 1, furthercomprising: a diode electrically connected to the lower electrode. 10.The PRAM device of claim 1, wherein the phase-change nanowire has adiameter of less than about 10 nm.
 11. The PRAM device of claim 1,wherein the lower and upper electrodes include at least one of aconductive material and a conductive carbon-based material.
 12. The PRAMdevice of claim 11, wherein the conductive material is at least one oftitanium, tantalum, tungsten, molybdenum, niobium, titanium nitride,tantalum nitride, tungsten nitride, molybdenum nitride, niobium nitride,molybdenum aluminum nitride, tungsten boron nitride, titaniumoxynitride, tungsten oxynitride and tantalum oxynitride.